Installing doors involve arranging for an opening in a wall wherein stud define a casing into which fit the door jamb. The door jamb is what holds a door by way of hinges. In order to conceal the spacing between the casing and the jamb, a door frame overlaps that section and acts as a decorative element for the door. The same applies of course to windows. Typically, jambs and frames are separate pieces that require varying degrees of cutting and adjustments. It is that cutting and adjustment that is time consuming and can also be badly done according to the ability of whoever does the work.